Whenever you have a trauma that you don't face right away, it gets more difficult to deal with as time goes on. You get used to pushing it away and it gets more comfortable for you. But I think even if your mind isn't thinking about it, your brain still is. Your brain shuts down your mind as a way of protecting you, so it pushes it away. Being that you are thinking about it again may be a signal of your mind's readiness to deal with the trauma. Maybe you could write down everything you remember, then contact others that know about the accident to clarify any questions you may have.
Dealing with it as an uncertain teenager may have been more difficult and now that you are a strong adult, your recovery may be smoother than you anticipate. As a young child I was abused and find that when the memories resurface as an adult I can handle them better now that I am not a scared little girl.
I think it your medical involvement (EMS/Fire/nursing) endeavors will help you heal as well. You have learned and still actively learn every day that some things are beyond your control and even if you were a doctor you wouldn't have been able to save her.
I would talk about the accident and research her injuries fully so you have a complete understanding of what happened. As a grown adult with a medical profession, I think it will help you heal and give you peace. But if it makes you uncomfortable in any way, contact a professional to deal with this. I'm not a doctor.
*As a side note~ My husband is a driver for our EMS and has been for 2 years. A few weeks ago our neighbor and dear friend had a heart attack. My husband did cpr on him until the medics got there and took over. Our neighbor died at the hospital and my husband felt like maybe there was something he should have done differently to change the outcome. After learning the circumstances surrounding his cause of death (aneurysm in aortic valve) he realized there was nothing he could have done and was able to let the guilt go. He had to get counseling for it though. Just one time of talking it out, but it really helped him to put things into perspective with a medical point of view and accept what happened.